1. Field of the Invention
The present invention relates to a liquid crystal cell and method of making the cell. The liquid crystal cell has a chamber for receiving a layer of liquid crystal material and the chamber is formed between a pair of plates whose facing surfaces are each provided with electrically conducting coatings and are joined together adjacent their edges by a hermetical, glass solder seal.
2. Prior Art
The life duration of a cell of a liquid crystal display is basically dependent on the quality of the seal between the plates which form the chamber for receiving the liquid crystal layer. Previously adhesives, such as hardenable synthetic resins, were used and have the advantage that they were relatively simple to handle. However, these synthetic resins would react irreversibly with the material of the liquid crystal layer and gradually allow both atmospheric moisture and atmospheric oxygen to penetrate into the cell to react with the material of the liquid crystal layer. Such a reaction with a liquid crystal layer will cause the layer to loose its desired quality and finally cause the liquid crystal cell to become unserviceable and inoperative. Another disadvantage with the synthetic resin seal is that at high operating temperatures, a danger exists that the material of the liquid crystal layer will leak out of the cell between one of the plates and the adhesive.
For these reasons, the use of glass solder has been recently adopted as a method of sealing the plates forming the chamber of the cell. A seal of this type will practically consist of only inorganic components and will not react or attack the material of the liquid crystal layer. Also, the glass solder provides long term protection from environmental influences. However, the use of glass solder as a seal requires a plurality of expensive and, in particular, time consuming production steps. For example, a solder paste, which is formed of pieces of glass solder and an organic binding agent, is applied to a surface of the plate by a silk screen printing process and in the desired pattern to form a frame of glass solder on the surface. Subsequent to applying the frame with a silk screen printing process, the glass solder frame is subjected to a premelting or preglazing process which involves heating to remove the organic binding agent and to fix the glass particles of the solder to the surface of the plate. This heating removes the organic bonding agent by a combustion process which does not leave any residue in the remaining glass solder frame. After the premelting or preglazing, a second plate is then placed on the frame to form an assembly which is then finally joined together in a second melting process to form a sealed chamber of the cell. Examples of these types of methods of forming a liquid crystal cell is disclosed in British Patent No. 1,387,677, which corresponds to German Offenlegungsschrift No. 2,254,940.
In the above-mentioned reference, spacing particles such as glass fibers or hard glass particles may be included in the glass solder paste. During the melting or fusing of the solder paste to form the seal, these spacing particles would remain substantially unchanged and provide permanent spacing elements to provide spacing between the plate members.